A stationary exercise device disclosed in the U.S. Pat. No. 5,383,829 is composed of a base which is provided in both sides of the front segment thereof with two guide rails, and in the rear segment thereof with a resisting wheel. A pivot of the resisting wheel is provided respectively at both ends thereof with a crank. The two guide rails are used to guide two slide wheels which are fastened with the undersides of the front ends of two connection rods. The two connection rods are provided respectively at the midsegment thereof with a pedal. The connection rods are fastened pivotally and respectively at the rear end thereof with the crank. As the pedals are operated by the feet of a person, the slide wheels are activated to move back and forth along the guide rails. In the meantime, the cranks are actuated to turn such that the resisting wheel is driven to rotate. As a result, the stationary exercise device is capable of providing a leg exercise similar in effect to the mountain-climbing.
Such a prior art exercise device as described above is defective in design in that the contact areas of the two slide wheels and the two guide rails are so small as to cause the slide wheels to wear out easily, thereby undermining the service life span of the exercise device. In addition, the construction of the prior art exercise device is complicated by the two guide rails which can not be easily mounted with precision. Moreover, the installation of the guide rails calls for the use of many accessories, thereby resulting in a substantial increase in the cost of making the stationary exercise device.